Known gas analysis systems also include one or more sample cells, for example one or more Herriot cells, for containing a gas sample to be analysed and through which a laser beam passes in order to interact with the gas sample. Arrangement of sample cells and other optical components affects the geometry, size and performance of a gas analysis system. In order for instance to make a system compact, for example to be able to contain the system within a compact, transportable housing, it can be important to provide a suitable arrangement of the sample cell and other optical components.